The present disclosure generally relates to a power management system. More specifically, the present disclosure relates to a power management system that eliminates the delay in supplying power to priority loads from either a secondary power source, such as a standby generator, or a utility power supply after switching between the two power supplies.
When there is a power outage, backup power may be provided by a standby generator. In some cases, the standby generator is started automatically after detection of the power outage. A standby generator that is started automatically usually requires an automatic transfer switch to connect electrical loads to the generator rather than to the utility power supply. A combination of a standby generator and an automatic transfer switch is generally installed by trained personnel.
Since the power supplied by the standby generator is limited by the size of the generator, the amperage rating of the generator can limit the types of and number of appliances that are connected to the standby generator during power outages. As an example, large appliances such as air conditioners, hot water heaters and on-demand appliances such as microwave ovens and toasters can draw a significant amount of power that, in combination, may exceed the rating limit for the standby generator.
Presently, automatic transfer switches are available that include a series of priority circuits that allow the automatic transfer switch to selectively reduce the load on the generator when the load approaches the rated limit for the generator. Typically, the priority circuits are assigned a value from 1 to a maximum number, where the circuit assigned priority value 1 has the highest priority. When the load on the generator approaches the rating for the generator, a control unit in the transfer switch begins to manage the load by opening switches or relays within a remote contactor to disconnect the load connected to the lowest priority circuit. Although the term “remote contactor” is used in the present disclosure, the term “remote contactor” signifies any type of module, node or internal components included directly in a power consuming device that allows the disconnection of the device from the source of electrical power. The automatic transfer switch continues to manage the loads from the lowest priority circuit to the highest priority circuit until the load reaches a preset limit to ensure that the generator can continue to provide power to the highest priority loads connected to the generator (without the risk of overloading and shutting down the generator, thus inconveniencing the end user). When the load on the generator is reduced, load managing ceases.
During initial installation of the standby generator and automatic transfer switch, installers connect loads to each of the priority circuits based upon a perceived importance of each of the loads. As an example, an air conditioner may be assigned to priority circuit 1 where a less important load, such as a pool pump, may be assigned to priority circuit 3. Thus, when the total load on the generator nears the rating for the generator, the pool pump connected to priority circuit 3 is managed before the air conditioner connected to priority circuit 1. Currently available systems from Briggs & Stratton allows for reprioritization of loads without rewiring by an electrician. In such systems, the priority of the loads can be dynamically adjusted in a control unit depending on the preference of the end user. Other manufactures rely upon fixed, hard wire connections to the priority circuits, which may require trained personnel.
In currently available power management systems, when the supply of utility power is interrupted, the control unit in the transfer switch opens all of the relays or switches in the remote contactors to disconnect all of the managed loads from the power distribution network. Once the managed loads are disconnected, the transfer switch activates the standby generator. Once the standby generator begins operation, the control unit contained within the transfer switch waits for a delay period, often times up to five minutes, before beginning to reconnect the managed loads to the standby generator in the priority order. The delay in providing power to the managed loads is seen by many users as a disadvantage of the power management system described.
Likewise, when utility power returns to the power management system, the control unit in the transfer switch initially opens the relays within all of the remote contactors prior to switching over to power supplied by the utility. Once the switch in the transfer switch has been transferred to the utility power supply from the standby generator, the control unit again delays before reclosing the switches within the remote contactors in the priority order. Once again, this delay can be up to five minutes. During the delay, each of the managed loads are unavailable for use, which can create an inconvenience to the user.